1. Field of the Invention
The present invention relates to an element for magnetic recording having a great resistance to wear and tear and, more particularly, to the use of a new class of compounds as lubricants for said elements.
2. The Prior Art
Elements used for magnetic recording most often comprise a non-magnetizable support to which is applied a layer of magnetizable particles dispersed in a binder usually comprising a synthetic resin.
It is known that in magnetic recording, and more particularly in the case of high density information storage, the magnetic heads must be in close contact with the magnetizable layer. As a result, phenomena occur that are connected with friction which can result in a more or less extensive change of the layer. An often observed mechanism consists in a tearing of material which, by accumulating on the head or heads, or by transferring to the surface of the tape, causes a weakening or even the disappearance of the signal.
These phenomena are particularly sensitive in the case of tapes that serve as memories in data processing and of tapes designed for video recording, due to the relatively high speeds between the heads and the magnetic layer and to the particular requirements connected with these types of usages.
A particularly strict test of magnetic tapes involves certain equipment for the recording and copying of images, wherein the track is scanned helically. Equipment of this type currently used in closed-circuit television broadcasting, and particularly in educational broadcasting, offers the possibility of still frame reading by immobilizing the tape while the head continues its scanning, so that it is always the same image being projected. Under these conditions, a small portion of the tape is subjected to wear and tear corresponding to several thousand passages per minute and the result is, in the case of an ordinary tape, a rapid deterioration of the layer with disappearance of the image.
Numerous solid lubricants have been suggested for extending the useful life of the tapes, e.g. graphite and molybdenum disulfide, but these give disappointing results in that only small amounts can be used without reducing the quality of the magnetic signal. The silicones, such as described in French patent No. 1,032,730, make it possible to improve resistance to abrasion in certain particular cases, but their efficiency is reduced when the relative speed of head and tape is high, particularly in the recording of images. The fatty acid esters of monoalcohols such as described in U.S. Pat. No. 3,274,111 constitute a class of outstanding lubricants, particularly for the recording of images, but certain difficulties in connection with the exudation of the lubricant can appear as is indicated in said patent. This exudation phenomenon results, in general, from the fact that many commercial esters, of fatty acids used in the manufacture of these esters, are formed by the mixture of different homologs that are difficult to separate, e.g. myristates, palmitates, stearates, and if, at the temperature that is used, some are liquid and some are solid, the first assist migration to the surface of the second, causing the observed formation of solid deposits.
In view of the foregoing, it should be obvious that the result achieved when a given material is used as a lubricant in a magnetic recording layer is both unpredictable and empirical in nature. This is further illustrated by Example 6 which follows.
Accordingly, it is an object of the present invention to remedy disadvantages obtained with the afore-cited lubricants, and to provide a new class of compounds useful as lubricants for magnetic recording elements and, more particularly, to provide a tape for magnetic recording having an improved resistance to wear and tear and thus a longer useful lifetime. Other objects of this invention will become apparent from an examination of the specification and claims that follow.